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  • Thread Safety of C# List<T> for readers

    - by ILIA BROUDNO
    I am planning to create the list once in a static constructor and then have multiple instances of that class read it (and enumerate through it) concurrently without doing any locking. In this article http://msdn.microsoft.com/en-us/library/6sh2ey19.aspx MS describes the issue of thread safety as follows: Public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe. A List can support multiple readers concurrently, as long as the collection is not modified. Enumerating through a collection is intrinsically not a thread-safe procedure. In the rare case where an enumeration contends with one or more write accesses, the only way to ensure thread safety is to lock the collection during the entire enumeration. To allow the collection to be accessed by multiple threads for reading and writing, you must implement your own synchronization. The "Enumerating through a collection is intrinsically not a thread-safe procedure." Statement is what worries me. Does this mean that it is thread safe for readers only scenario, but as long as you do not use enumeration? Or is it safe for my scenario?

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  • Django repeating vars/cache issue?

    - by Mark
    I'm trying to build a better/more powerful form class for Django. It's working well, except for these sub-forms. Actually, it works perfectly right after I re-start apache, but after I refresh the page a few times, my HTML output starts to look like this: <input class="text" type="text" id="pickup_addr-pickup_addr-pickup_addr-id-pickup_addr-venue" value="" name="pickup_addr-pickup_addr-pickup_addr-pickup_addr-venue" /> The pickup_addr- part starts repeating many times. I was looking for loops around the prefix code that might have cause this to happen, but the output isn't even consistent when I refresh the page, so I think something is getting cached somewhere, but I can't even imagine how that's possible. The prefix car should be reset when the class is initialized, no? Unless it's somehow not initializing something? class Form(object): count = 0 def __init__(self, data={}, prefix='', action='', id=None, multiple=False): self.fields = {} self.subforms = {} self.data = {} self.action = action self.id = fnn(id, 'form%d' % Form.count) self.errors = [] self.valid = True if not empty(prefix) and prefix[-1:] not in ('-','_'): prefix += '-' for name, field in inspect.getmembers(self, lambda m: isinstance(m, Field)): if name[:2] == '__': continue field_name = fnn(field.name, name) field.label = fnn(field.label, humanize(field_name)) field.name = field.widget.name = prefix + field_name + ife(multiple, '[]') field.id = field.auto_id = field.widget.id = ife(field.id==None, 'id-') + prefix + fnn(field.id, field_name) + ife(multiple, Form.count) field.errors = [] val = fnn(field.widget.get_value(data), field.default) if isinstance(val, basestring): try: val = field.coerce(field.format(val)) except Exception, err: self.valid = False field.errors.append(escape_html(err)) field.val = self.data[name] = field.widget.val = val for rule in field.rules: rule.fields = self.fields rule.val = field.val rule.name = field.name self.fields[name] = field for name, form in inspect.getmembers(self, lambda m: ispropersubclass(m, Form)): if name[:2] == '__': continue self.subforms[name] = self.__dict__[name] = form(data=data, prefix='%s%s-' % (prefix, name)) Form.count += 1 Let me know if you need more code... I know it's a lot, but I just can't figure out what's causing this!

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  • MySQL asking a user for SUPER privilege to perform a delete.

    - by Fran
    Hello, When trying to do a delete operation on a table, mysql reports the following error: Error code 1227: Access denied; you need the SUPER privilege for this operation. However, my user has this privilege granted for all tables in the schema: GRANT ALL PRIVILEGES ON myschema.* TO 'my_admin'@'%' How come it asks me for SUPER privilege for a delete? Thanks in advance.

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  • Oracle 10 g - Unable to free up space in tablespace

    - by Bruno Rothgiesser
    The tablespace in Oracle 10g is almost 100% used. Size (MB) = 571,768.0 Used (MB) = 571,534.0 I just deleted (and committed) thousands of records in a table that belongs to a schema associated with that tablespace. Surprisingly, no space was freed up according to the Tablespaces page on Enterprise Manager. Question: is there anything that I need to do to force Oracle to release the space corresponding to the deleted records?

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  • Sparsity Failure

    - by Lijo
    Hi Team, In the context of data warehouse, could you please explain "Sparsity Failure" of aggregate tables? It would be great if you can explain it with product sales in a store; aggregated by week. It could be easily understood if it is having schema as well as sample data. Thanks Lijo

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  • Is something along the lines of nested memoization needed here?

    - by Daniel
    System.Transactions notoriously escalates transactions involving multiple connections to the same database to the DTC. The module and helper class, ConnectionContext, below are meant to prevent this by ensuring multiple connection requests for the same database return the same connection object. This is, in some sense, memoization, although there are multiple things being memoized and the second is dependent on the first. Is there some way to hide the synchronization and/or mutable state (perhaps using memoization) in this module, or perhaps rewrite it in a more functional style? (It may be worth nothing that there's no locking when getting the connection by connection string because Transaction.Current is ThreadStatic.) type ConnectionContext(connection:IDbConnection, ownsConnection) = member x.Connection = connection member x.OwnsConnection = ownsConnection interface IDisposable with member x.Dispose() = if ownsConnection then connection.Dispose() module ConnectionManager = let private _connections = new Dictionary<string, Dictionary<string, IDbConnection>>() let private getTid (t:Transaction) = t.TransactionInformation.LocalIdentifier let private removeConnection tid = let cl = _connections.[tid] for (KeyValue(_, con)) in cl do con.Close() lock _connections (fun () -> _connections.Remove(tid) |> ignore) let getConnection connectionString (openConnection:(unit -> IDbConnection)) = match Transaction.Current with | null -> new ConnectionContext(openConnection(), true) | current -> let tid = getTid current // get connections for the current transaction let connections = match _connections.TryGetValue(tid) with | true, cl -> cl | false, _ -> let cl = Dictionary<_,_>() lock _connections (fun () -> _connections.Add(tid, cl)) cl // find connection for this connection string let connection = match connections.TryGetValue(connectionString) with | true, con -> con | false, _ -> let initial = (connections.Count = 0) let con = openConnection() connections.Add(connectionString, con) // if this is the first connection for this transaction, register connections for cleanup if initial then current.TransactionCompleted.Add (fun args -> let id = getTid args.Transaction removeConnection id) con new ConnectionContext(connection, false)

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  • Can't add a .ldif to OpenLDAP, recent version (no slapd.conf)

    - by Biganon
    I'm new to LDAP and I'm trying to add the mmc.ldif and mail.ldif files that come with Mandriva Directory Server to my LDAP configuration, using the command : ldapadd -x -W -D "cn=admin,dc=biganon,dc=com" -f schema/mmc.ldif I then give the admin password I've set during slapd installation but get this error : ldap_bind: Invalid credentials (49) I have no slapd.conf file. I'm on Debian 6.0.1, OpenLDAP 2.4.23 Thank you

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  • Codeigniter Inserting Multidimensional Array as rows in MySQL

    - by RisingSun
    Please Refer to this question I asked Codeigniter Insert Multiple Rows in SQL To restate <tr> <td><input type="text" name="user[0][name]" value=""></td> <td><input type="text" name="user[0][address]" value=""><br></td> <td><input type="text" name="user[0][age]" value=""></td> <td><input type="text" name="user[0][email]" value=""></td> </tr> <tr> <td><input type="text" name="user[1][name]" value=""></td> <td><input type="text" name="user[1][address]" value=""><br></td> <td><input type="text" name="user[1][age]" value=""></td> <td><input type="text" name="user[1][email]" value=""></td> </tr> .......... Can Be Inserted into MySQL as this foreach($_POST['user'] as $user) { $this->db->insert('mytable', $user); } This results in multiple MySQL queries. Is it possible to optimise it further, so that the insert occurs in one query Something like this insert multiple rows via a php array into mysql but taking advantage of codeigniters simpler syntax. Thanks

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  • If attacker has original data, and encrypted data, can they determine the passphrase?

    - by Brad Cupit
    If an attacker has several distinct items (for example: e-mail addresses) and knows the encrypted value of each item, can the attacker more easily determine the secret passphrase used to encrypt those items? Meaning, can they determine the passphrase without resorting to brute force? This question may sound strange, so let me provide a use-case: User signs up to a site with their e-mail address Server sends that e-mail address a confirmation URL (for example: https://my.app.com/confirmEmailAddress/bill%40yahoo.com) Attacker can guess the confirmation URL and therefore can sign up with someone else's e-mail address, and 'confirm' it without ever having to sign in to that person's e-mail account and see the confirmation URL. This is a problem. Instead of sending the e-mail address plain text in the URL, we'll send it encrypted by a secret passphrase. (I know the attacker could still intercept the e-mail sent by the server, since e-mail are plain text, but bear with me here.) If an attacker then signs up with multiple free e-mail accounts and sees multiple URLs, each with the corresponding encrypted e-mail address, could the attacker more easily determine the passphrase used for encryption? Alternative Solution I could instead send a random number or one-way hash of their e-mail address (plus random salt). This eliminates storing the secret passphrase, but it means I need to store that random number/hash in the database. The original approach above does not require this extra table. I'm leaning towards the the one-way hash + extra table solution, but I still would like to know the answer: does having multiple unencrypted e-mail addresses and their encrypted counterparts make it easier to determine the passphrase used?

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  • mysqldump is not dumping my data

    - by oompahloompah
    I am running mysqldump on Ubuntu Linux (10.0.4 LTS) my mySQL version info is: mysql Ver 14.14 Distrib 5.1.41, for debian-linux-gnu (i486) using readline 6.1 I used the following command: mysql -u username -p dbname dbname_backup.sql However when I opened the generated .sql file, I saw that most of the tables had only the schema dumped and in the few cases where the actual data was dumped, only 1 or two records were dumped (there are ATLEAST several tens of records in each table). Does anyone know what maybe going on?

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  • Retrieve MS SQL database or table structure in XML

    - by clutch
    Is there a way to export the database schema in well formed XML of a MS 2000 SQL Server. I'm looking for just the structure not the data and the more detailed the better. The XML may be used in a migration processes. I'm more familiar with MySQL then with SQL Server so please be detailed if you have time. Thanks

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  • Modeling many-to-one with constraints?

    - by Greg Beech
    I'm attempting to create a database model for movie classifications, where each movie could have a single classification from each of one of multiple rating systems (e.g. BBFC, MPAA). This is the current design, with all implied PKs and FKs: TABLE Movie ( MovieId INT ) TABLE ClassificationSystem ( ClassificationSystemId TINYINT ) TABLE Classification ( ClassificationId INT, ClassificationSystemId TINYINT ) TABLE MovieClassification ( MovieId INT, ClassificationId INT, Advice NVARCHAR(250) -- description of why the classification was given ) The problem is with the MovieClassification table whose constraints would allow multiple classifications from the same system, whereas it should ideally only permit either zero or one classifications from a given system. Is there any reasonable way to restructure this so that a movie having exactly zero or one classifications from any given system is enforced by database constraints, given the following requirements? Do not duplicate information that could be looked up (i.e. duplicating ClassificationSystemId in the MovieClassification table is not a good solution because this could get out of sync with the value in the Classification table) Remain extensible to multiple classification systems (i.e. a new classification system does not require any changes to the table structure)? Note also the Advice column - each mapping of a movie to a classification needs to have a textual description of why that classification was given to that movie. Any design would need to support this.

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  • JPA + EJB + JSF: how can design complicated query

    - by Harry Pham
    I am using netbean 6.8 btw. Let say that I have 4 different tables: Company, Facility, Project, and Document. So the relationship is this. A company can have multiple facilities. A facility can have multiple projects, and a project can have multiple documents. Company: +companyNum: PK +facilityNum: FK Facility: +facilityNum: PK +projectNum: FK Project: +projectNum: PK +drawingNum: FK So when I create Entity Class From Database in netbean 6.8, I have 4 entity classes that named after the above 4 tables. So if I want to see all the Document in the database, then it is easy. In my SessionBean, I would do this: @PersistenceContext private EntityManager em; List<Document> documents = em.createNamedQuery("Document.findAll").getResultList(); However, that is not all what I need. Let say that I want to know all the Document from a particular Company, or all the Document from a particular Project from a particular Facility from a particular Company. I am very new to JPA + EJB + JSF as a whole. Please help me out.

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  • VB app to web service

    - by brandon
    I know very little about web service but I assumed it would be the solution I was looking for. Basically I made an application in VB that I want to be ubiquitous for a lack of a better word. I need it to receive requests from multiple users and respond all at once. I was told "technically if you write a webservice you can provide as many results back to users as are connected." Maybe there is another solution for me that will give me the results I want. Here is an example of what I'm trying to do. Lets say I make an application in VB that does math. I now make a website. My website allows for a person to input 1 + 1 they click submit and my website then connects to my VB application running on my server listening for a request. It accepts the request from my website, and then it solves the math problem and returns the answer back to the website "1 + 1 = 2" That is only an example of the type of thing I need. My problem is that I can't have multiple people visiting my website all connecting to that same application running on my server so somehow I need the application to be where it can be accessed by multiple users. I was told a web service would be the answer but if there is another solution I'd like to know. If the only solution is a web service, then how can I manage to either convert the VB app to a web service? Can I have to convert the app to asp.net or some other language? Is there an easier option?

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  • How can I split abstract testcases in JUnit?

    - by Willi Schönborn
    I have an abstract testcase "AbstractATest" for an interface "A". It has several test methods (@Test) and one abstract method: protected abstract A unit(); which provides the unit under testing. No i have multiple implementations of "A", e.g. "DefaultA", "ConcurrentA", etc. My problem: The testcase is huge (~1500 loc) and it's growing. So i wanted to split it into multiple testcases. How can organize/structure this in Junit 4 without the need to have a concrete testcase for every implementation and abstract testcase. I want e.g. "AInitializeTest", "AExectueTest" and "AStopTest". Each being abstract and containing multiple tests. But for my concrete "ConcurrentA", i only want to have one concrete testcase "ConcurrentATest". I hope my "problem" is clear. EDIT Looks like my description was not that clear. Is it possible to pass a reference to a test? I know parameterized tests, but these require static methods, which is not applicable to my setup. Subclasses of an abstract testcase decide about the parameter.

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  • .NET 4 ... Parallel.ForEach() question

    - by CirrusFlyer
    I understand that the new TPL (Task Parallel Library) has implemented the Parallel.ForEach() such that it works with "expressed parallelism." Meaning, it does not guarantee that your delegates will run in multiple threads, but rather it checks to see if the host platform has multiple cores, and if true, only then does it distribute the work across the cores (essentially 1 thread per core). If the host system does not have multiple cores (getting harder and harder to find such a computer) then it will run your code sequenceally like a "regular" foreach loop would. Pretty cool stuff, frankly. Normally I would do something like the following to place my long running operation on a background thread from the ThreadPool: ThreadPool.QueueUserWorkItem( new WaitCallback(targetMethod), new Object2PassIn() ); In a situation whereby the host computer only has a single core does the TPL's Parallel.ForEach() automatically place the invocation on a background thread? Or, should I manaully invoke any TPL calls from a background thead so that if I am executing from a single core computer at least that logic will be off of the GUI's dispatching thread? My concern is if I leave the TPL in charge of all this I want to ensure if it determines it's a single core box that it still marshalls the code that's inside of the Parallel.ForEach() loop on to a background thread like I would have done, so as to not block my GUI. Thanks for any thoughts or advice you may have ...

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  • Fetching only the first record in the table (via the view) without changing controller?

    - by bgadoci
    I am trying to only fetch the first record in my table for display. I am creating a site where a user can upload multiple images and attach to a post but I only want to display the first image view for each post. For further clarification posts belong_to projects. So when you are on the projects show page you see multiple posts. In this view I only want to display the first image for each post. Is there a way to do this in the view without affecting the controller (as later I want to allow users to browse all photos through the addition of a lightbox). Here is my /views/posts/_post.html.erb code: <% div_for post do %> <% post.photos.each do | photo | %> <%= image_tag(photo.data.url(:large), :alt => '') %> <%= photo.description %> <% end unless post.photos.first.new_record? rescue nil %> <%= link_to h(post.link_title), post.link %> <%= h(post.description) %> <%= link_to 'Manage this post', edit_post_path(post) %> <% end %> UPDATE: I am using a photos model to attach multiple photos to each post and using paperclip here.

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  • How can I improve this SQL to avoid several problems with its results?

    - by Josh Curren
    I am having some problems with trying to search. Currently this will only return results that have at least 1 row in the maintenance_parts table. I would like it to return results even if there are 0 parts rows. My second problem is that when you search for a vehicle and it should return multiple results (multiple maintenance rows) it will only return 1 result for that vehicle. Some Background Info: The user has 2 fields to fill out. The fields are vehicle and keywords. The vehicle field is meant to allow searching based on the make, model, VIN, truck number (often is 2 - 3 digits or a letter prefix followed by 2 digits), and a few other fields that belong to the truck table. The keywords are meant to search most fields in the maintenance and maintenance_parts tables (things like the description of the work, parts name, parts number). The maintenance_parts table can contain 0, 1, or more rows for each maintenance row. The truck table contains exactly 1 row for every maintenance row. A truck can have multiple maintenance records. "SELECT M.maintenance_id, M.some_id, M.type_code, M.service_date, M.mileage, M.mg_id, M.mg_type, M.comments, M.work_done, MATCH( M.comments, M.work_done) AGAINST( '$keywords' ) + MATCH( P.part_num, P.part_desc, P.part_ref) AGAINST( '$keywords' ) + MATCH( T.truck_number, T.make, T.model, T.engine, T.vin_number, T.transmission_number, T.comments) AGAINST( '$vehicle' ) AS score FROM maintenance M, maintenance_parts P, truck T WHERE M.maintenance_id = P.maintenance_id AND M.some_id = T.truck_id AND M.type_code = 'truck' AND ( (MATCH( T.truck_number, T.make, T.model, T.engine, T.vin_number, T.transmission_number, T.comments) AGAINST( '$vehicle' ) OR T.truck_number LIKE '%$vehicle%') OR MATCH( P.part_num, P.part_desc, P.part_ref) AGAINST( '$keywords' ) OR MATCH( M.comments, M.work_done) AGAINST( '$keywords' ) ) AND M.status = 'A' GROUP BY maintenance_id ORDER BY score DESC, maintenance_id DESC LIMIT 0, $limit"

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  • Basic Application Organization + Publishing (.NET 4.0)

    - by keynesiancross
    Hi all, I'm trying to figure out the best way to keep my program organized. Currently I have many class files in one project file, but some of these classes do things that are very different, and some I would like to expose to other applications in the future. One thought I had to organizing my application was to create multiple project files, with one "Main" project, which would interact with all the other projects and their relevant classes as needed. Does this make sense? I was wondering if anyone had any suggestions in regards to using multiple project files in one solution (and how do you create something like this?), and if it makes sense to have multiple namespaces in one solution... Cheers ----Edit Below---- Sorry, my fault. Currently my program is all in one console project. Within this project I have several classes, some of which basically launch a BackgroundWorker and run an endless loop pulling data. The BackgroundWorker then passes this data back to the main business logic as needed. I'm hoping to seperate this data pull material (including the background worker material) into one project file, and the rest of the business logic into another project file. The projects will have to pass objects between eachother though (the data to the main business logic, and the business logic will pass startup parameteres to the dataPull project)... Hopefully this adds a bit more detail.

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  • TCP/IP Implementation General Questions

    - by user2971023
    I've implemented the concepts shown here; http://wiki.unity3d.com/index.php/Simple_TCP/IP_Client_-_Server outside of unity and it works. (though i had to create the TCPIPServerApp from scratch as i could not find the base project anywhere). I have some general questions on how to use tcp/ip properly however. I've done some research on tcp/ip itself but I'm still a little confused. It seems like using the method above doesn't guarantee that I'll see the message (res). It just checks on every update to see if there is a different message in res. What if multiple messages are sent and the program lags or something, will i miss the earlier packet(s)? Should i instead do an array so it stores the last X messages? How do i know the data was received? Do I need to add a message id and build in my own ack into the data? Should i check to see if the port is in use before setting up a connection? Sorry for all the questions. This is all new to me but I enjoy this very much! ... Below already answered By Anton, Thanks It sounds like tcp uses its own packet numbering to ensure the packets end up in the right order on the other side. What if a packet is missed, are the subsequent packets thrown away? Or is this numbering and packet ordering, only for handling data that is broken out into multiple packets? TCP will automatically break the data into multiple packets if necessary right?

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  • listbox select count not work dont work

    - by sadpcd
    I recently trying to make a form with multiple select box. When someone select the options the number of selected options will be display on another text. I'm a beginner in JavaScript. The function is called, but it doesn't count the number of the selected options. <select name="element_17_1[ ]" size="7" multiple="multiple" class="element select medium" id="element_17_1[ ]" onfocus="selectCount(this.form);" onClick="selectCount(this.form);" > <option value="Opt1">Opt1</option> <option value="Opt2">Opt2</option> <option value="Opt3">Opt3</option> <option value="Opt4">Opt4</option> <option value="Opt5">Opt5</option> <option value="Opt6">Opt6</option> <option value="Opt7">Opt7</option> </select> and this is the function I tried in the <head> function selectCount(f) { var selObj = myForm.elements['element_17_1[]']; var totalChecked = 0; for (i = 0; i < selObj.options.length; i++) { if (selObj.options[i].selected) { totalChecked++; } } f.element_9.value = totalChecked; }

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  • LINQ Many to Many With In or Contains Clause (and a twist)

    - by Chris
    I have a many to many table structure called PropertyPets. It contains a dual primary key consisting of a PropertyID (from a Property table) and one or more PetIDs (from a Pet table). Next I have a search screen where people can multiple select pets from a jquery multiple select dropdown. Let's say somebody selects Dogs and Cats. Now, I want to be able to return all properties that contain BOTH dogs and cats in the many to many table, PropertyPets. I'm trying to do this with Linq to Sql. I've looked at the Contains clause, but it doesn't seem to work for my requirement: var result = properties.Where(p => search.PetType.Contains(p.PropertyPets)); Here, search.PetType is an int[] array of the Id's for Dog and Cat (which were selected in the multiple select drop down). The problem is first, Contains requires a string not an IEnumerable of type PropertyPet. And second, I need to find the properties that have BOTH dogs and cats and not just simply containing one or the other. Thank you for any pointers.

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